To couple a twin-belt casting machine in tandem with a regular rolling mill, in contrast with a planetary mill, for continuously casting steel product, the twin-belt caster must be operated at high speed for reasons explained in the next paragraph. This term "high speed" is intended to mean a linear output rate of at least 300 inches per minute (25 feet per minute).
When a hot cast steel slab enters a regular rolling mill at a significant lesser speed than defined above, there occurs undue transfer of heat from the product being rolled into the localized region of each mill roll in contact with the product. Thus, too much cooling of product occurs before exiting the rolling mill, and the rolls themselves become adversely affected by localized overheating of the working surfaces.
U.S. Pat. No. 2,640,235 disclosed cooling chambers or water jackets (44, 45, 46, 48, 49 and 50 as numbered in FIGS. 1, 5, 7 and 8 therein) adjacent to the outer surfaces of transversely bowed casting belts in the entrance section of a twin-belt caster. Other cooling chambers or water jackets (56 and 59 in FIGS. 1, 2 and 2a) were adjacent to the casting belts in the casting section of this machine. For preventing the pressure of the cooling water in these latter chambers from distorting the belts, electromagnetic attraction held the belts against non-magnetic copper or brass spacers (58 or 58a). Steering of each belt was accomplished, as shown in FIG. 6 therein, by twisting the orientation of the upstream pulley roller (19) about the axis of the belt-tensioning piston rod (21). It is noted in FIG. 1 and FIG. 9 of the above-mentioned patent that both casting belts (17 and 18) diverged away from the cast product before the belts had reached the respective downstream pulley rollers (25 and 40), which served as the belt drive rollers.
U.S. Pat. No. 2,904,860 showed the casting belts (14 and 16) extending adjacent to the cast product all of the way to the respective downstream pulley roller (130 and 122 in FIG. 2 therein). However, this caster included four pulley rollers (126, 134, 130 and 142 in FIG. 2 therein) for the upper casting belt (14) and three pulley rollers (118, 206 and 122) for the lower casting belt (16). Steering of the belts to run centrally was accomplished as shown in FIGS. 2 and 6 therein be skewing the axis of an intermediate roller (142 or 206, sometimes called a "third roller)" away from transverse relationship to the belt passing in contact with the respective steering roller. This third-roll steering arrangement depended in large measure upon frictional contact between the passing belt and the steering roller itself and was not fully effective or reliable due to variations in the coefficient of friction and in thermal conditions and minor imperfections in belt shape.
U.S. Pat. No. 3,036,348, and the related U.S. Pat. No. 3,123,874 disclosed a twin-belt caster wherein the upper casting belt (20 in FIG. 3 and FIG. 12 in 3,036,348) diverged from the cast product a considerable distance upstream from the exit pulley roll (78 in FIG. 12 of 3,036,348). Steering of the upper casting belt was accomplished by tilting the axis of the exit pulley roll (78) in a plane perpendicular to the plane of the casting region. The divergence of the upper casting belt from the cast product provided clearance for such exit pulley roll steering action. In this machine shown in U.S. Pat. No. 3,036,348 the lower casting belt (22) was steered by tilting the axis of the lower upstream pulley roll (80) in a plane perpendicular to the casting plane. FIGS. 13A and 13B therein explain the steering action produced by such tilting of the axis of a pulley roll.
U.S. Pat. No. 3,167,830 disclosed a steering arrangement similar to that for the upper belt in U.S. Pat. No. 3,036,348 wherein the axis of the exit pulley roll was tilted in a plane perpendicular to the plane of the casting region, except that in U.S. Pat. No. 3,167,830 the axes of both exit pulley rolls were tilted for steering the respective belts. In FIGS. 3, 6 and 7 of U.S. Pat. No. 3,167,830 was shown a smaller diameter belt back-up roller (46) positioned very close to the entrance pulley rolls (28 and 30). The other belt back-up rollers (44) were larger in diameter than this first back-up roller (46).
U.S. Pat. No. 3,310,849 described a four pulley roll arrangement for both belts in a twin-belt caster. Steering of a belt was obtained by simultaneously tilting the axis of both downstream pulley rolls, as shown in FIGS. 7 and 8 therein, in a plane perpendicular to the casting plane. It is noted in FIGS. 2 and 7 therein that the casting belts diverged from the cast product before reaching the exit pulley rolls (22) and (26) in order to provide clearance for the belt steering action.
U.S. Pat. No. 3,878,883 and related U.S. Pat. Nos. 3,949,805 and 3,963,068 disclosed steering apparatus for tilting the axis (144 in FIGS. 16, 17 and 18) of the exit pulley roll (22 or 18) in a plane perpendicular to the casting plane.
FIGS. 1, 2 and 3 herein illustrate the relationships involved in such prior art belt steering arrangements where the axis of each exit pulley roll 20 and 22 was tilted, as shown in FIGS. 2 and 3 herein, in a plane perpendicular to the plane of the casting region C for steering the respective upper and lower casting belts 24 and 26. After each casting belt 24 and 26 had progressed past the last back-up roller 28, it was necessary to diverge the belt away from the casting plane C to provide clearance with respect to the exiting cast product P. This clearance was necessary, as illustrated by FIG. 2, for allowing tilting (angle .theta.) of the exit pulley rolls 20 and 22 without causing them or the revolving belts to disturb the freshly cast product P exiting from the twin-belt machine.
In the machine of U.S. Pat. No. 2,904,860, steering was accomplished by a third roller as shown in FIG. 6 of that patent. Thus, it was not necessary for the casting belts to diverge from the exiting cast product. However, such third roller steering action was not entirely satisfactory for reasons as discussed above.